1. Field of the Invention
The present invention relates to an optical disk recording/reproducing device for recording a signal on a disk using a laser irradiated from an optical pickup, and for reproducing a signal recorded on a disk using a laser.
2. Description of the Background Art
Disk players which use an optical pickup to read signals recorded on a disk are widely used. Recently, optical disk recording/reproducing devices have also become commercially available. These devices are designed for performing, in addition to reproduction, recording of signals on a disk by a laser irradiated from an optical pickup.
In a typical optical disk recording/reproducing device, data is recorded by using a laser to create a series of pits on a disk. When the laser output is inappropriate, the pit size becomes too large or too small. To prevent this problem, a disk used in an optical disk recording/reproducing device includes a trial writing region on the innermost track side. After recording a signal in the trial writing region, the signal is reproduced and detected, and the laser output for recording is set according to the detected signal. This technique is disclosed, for example, in Japanese Patent Laid-Open Publication No. Hei 6-76288.
Recording of a signal on a disk is executed by alternately switching the level of the laser output from a laser element between a recording level and a reproducing level. A signal is recorded on a disk by creating a pit in a signal track on the disk using such a laser having an output level for recording, and the pit is formed in a prescribed size. The signal recording operation is executed while rotating the disk at a predetermined constant linear velocity. In some recently commercialized optical disk recording/reproducing devices, the linear velocity for the rotation during signal recording operation can be increased to several times the predetermined linear velocity.
When switching from the reproducing mode to the recording mode in an optical disk recording/reproducing device allowing re-recording, the switching speed is required to be correspondingly high in accordance with the servo operation of the servo circuit integrated in the laser driving circuit. As the recording speed of signals on the disk is increased, the switching operation from the reproducing mode to the recording mode must be executed in a shorter time. To accomplish this, it is necessary that recording be immediately restarted at an optimal laser output, especially when recording is resumed after an interruption.
To perform the switching operation in a reduced time, the method of increasing the gain of the servo circuit may be adopted. However, this method generates overshoot in the recording waveform at the start of recording. In addition to requiring time to start an optimal recording operation, there exists the problem of generation of abnormality in the recording signal.
An object of the present invention is to provide a laser output control circuit overcoming the above problems for use in an optical disk recording/reproducing device.
According to the present invention, there is provided an optical disk recording/reproducing device in which an optimal laser output is set while recording a test signal in a trial writing region provided on a disk, the device comprising a storage unit for storing data of the optimal laser output obtained when the optimal laser output is set, wherein, during a normal recording operation, a laser output signal is generated according to a laser output feedback control signal, and, when transferring from a reproducing operation to a recording operation, the feedback control is prohibited while the laser output signal is generated based on the optimal laser output data stored in the storage unit.
In the present device, the feedback control is prohibited when transferring from a reproducing operation to a recording operation, and the laser output signal is generated based on the previously stored optimal laser output data. In this way, the recording operation can immediately be started after the transfer. If the laser output signal is generated under feedback control after transfer in the same manner as during a normal recording operation, recording cannot be started until the feedback control stabilizes. However, according to the present invention as described above, the transfer from the reproducing mode to the recording mode can be executed in an extremely short time, allowing the transfer to be smoothly performed in accordance with the increased disk recording speed.
Further, generation of overshoot in the recording waveform can be prevented because the gain of the feedback loop, namely, the servo circuit, need not be increased merely to speed up the start of recording. The optimal laser output data used at the time of transfer is the data obtained during a recording into the trial writing region of the disk. Using this data, execution of recording in an appropriate recording condition can begin immediately after the transfer.
Moreover, because the present invention enables instantaneous transfer to the recording mode, with the present invention, recording can be smoothly performed in a connecting portion in which a signal is to be recorded immediately in succession to a previously recorded signal after an interruption in recording.
According to a further aspect of the present invention, in an optical disk recording/reproducing device as described above, while the laser output signal is generated from the optimal laser output data, the feedback control is prohibited when transferring from the reproducing operation to the recording operation, and the prohibition of the feedback control is canceled after a predetermined time period.
In this way, the feedback control is resumed after a predetermined time period subsequent to the transfer from the reproducing operation to the recording operation. After completing the quick transfer from the reproducing mode to the recording mode, recording operation can be performed in a stable manner through the feedback control.
In another aspect of the present invention, in an optical disk recording/reproducing device such as those described above, the feedback control signal is a monitor signal of a laser irradiated by a laser element. The device further comprises a comparator circuit for comparing the monitor signal to the optimal laser output data, an initial recording data storage unit for storing, as an initial recording data, a data obtained through amplification of the optimal laser output data by the comparator circuit, and an output switch for supplying, to a laser driving circuit for driving the laser element, an output from the comparator circuit and an output from the initial recording data storage unit in a selective manner by switching between the two outputs.
In a further aspect of the present invention, an optical disk recording/reproducing device such as those described above further comprises a comparative output control switch which opens and closes to switch between short-circuit and insulation between two ends of a capacitor provided in a feedback path of the comparator circuit. When operation is transferred from the reproducing operation to the recording operation, the output switch is switched to the side for outputting from the initial recording data storage unit, and the comparative output control switch is closed to short-circuit the two ends of the capacitor.
According to still another aspect of the present invention, in an optical disk recording/reproducing device such as those described above, the feedback control signal is a monitor signal of a laser irradiated by a laser element. The device further comprises a comparator circuit for comparing the monitor signal to the optimal laser output data from the storage unit, and a comparative output control switch which opens and closes to switch between short-circuit and insulation between two ends of a capacitor provided in a feedback path of the comparator circuit. When operation is transferred from the reproducing operation to the recording operation, the comparative output control switch is closed to short-circuit the two ends of the capacitor, thereby allowing the comparator circuit to output said optimal laser output data obtained from the storage unit.
By employing a switch for controlling the circuit state between the two ends of the capacitor, recording can be started using the optimal laser output data at the point operation is transferred from the reproducing operation to the recording operation. In addition, this simple arrangement allows a smooth transfer back to the feedback control.
More specifically, when transferring from the non-feedback control mode to the feedback control mode, the comparative output control switch is switched from the closed state to the open state. Immediately after the switching to the open state, no charge is accumulated in the capacitor. The comparator circuit therefore continues outputting the stored optimal laser output data being input to the comparator circuit. When the capacitor is charged to a predetermined level, the comparator circuit outputs a result of comparison between the feedback control signal and the optimal laser output data. During the period until the capacitor becomes charged to a predetermined level, recording operation can be performed in a stable manner using the optimal laser output data. In this way, use of the capacitor prevents an immediate transfer back to the feedback control mode which may cause a sudden change in the laser output, and achieves a smooth transfer back to the feedback control mode.